Twenty three years after the description of the Adult Respiratory Distress Syndrome the mortality in patients continues to exceed 50% despite many technological advances in supportive care. Sepsis is a major risk factor for ARDS and it is an important complication causing late mortality in patients with established ARDS. Many of the manifestations of sepsis are a consequence of the interaction of bacterial lipopolysaccharide (endotoxin, LPS) with responding cells that produce important inflammatory mediators. The purpose of this proposal is to improve our understanding of the important cellular events that contribute to the pathogenesis of LPS-mediated inflammatory reactions in the lungs. Specifically, we will investigate the importance of a novel LPS-binding protein (LBP) in LPS mediated inflammatory reactions in the lungs of humans and animals. We have shown that LBP is present in lung fluids of patients with ARDS and that it augments the effects of LPS on human and rabbit alveolar macrophages (AM). We propose to extend these observations by investigating the following important questions relevant to lung inflammation: 1.) For which AM-derived cytokines does LBP have a stimulatory effect and does the state of activation of the AM modify the effects of LBP? 2.) What types of inflammatory responses are associated with the greatest accumulation of LBP in the lungs e.g. ARDS, infections (pneumonia), chronic inflammatory diseases (sarcoidosis, interstitial fibrosis) and is the LBP that accumulates in the lungs bioactive? 3.) Does LBP affect interations between alveolar macrophages and whole bacteria? 4.) Is it possible to inhibit the effects of LBP on AM and thereby modify cytokine production by AM? We will measure LPS-driven cytokine production at the cellular and molecular level using AM from humans and rabbits. We will measure LBP in lung fluids from individuals with a variety of lung diseases to better understand the circumstances in which LBP plays a role in lung inflamma- tion. We hypothesize that LBP will accumulate in lung fluids when lung epithelial permeability is altered, but not when epithelial permeability is normal. We will determine whether the effects of LBP on free LPS are also seen when LBP interacts with whole organisms and we will investigate whether antibodies to LBP or CD14, a cellular receptor for LBP:LPS complexes, can be used to inhibit the effects of LBP:LPS complexes on AM. The results of these studies may lead to new strategies for therapy in patients with sepsis and ARDS.